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Herberton Mineral Field - Great Northern, Baal Gammon, Isabel
Queensland, Qld, Australia
Main commodities: Cu Ag Sn In


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The Herberton Mineral Field includes the Baal Gammon and Isabel Cu-Ag-Sn-In polymetallic deposits which are located ~6 km west and 3 km SSW respectively of the town of Herberton in North Queensland, Australia and are ~5 km apart (#Location: 17° 22' 56"S, 145° 19' 37"E).

Tin was first discovered in the Herberton Mineral Field in 1875, with active mining beginning by ~1880 (Dash et al., 1991). Since then >76 300 tonnes of tin metal have been produced from >2000 mines and diggings of various sizes. The principal historic activity was between 1880 and 1930, but continued until 1985. The initial discovery was of the Great Northern Lode in Herberton which comprised an ~1 m wide vein that could be traced for near 3 km. Over the first 15 years the Great Northern Mine treated ore from tis lode with a grade that averaged 14% Sn, but after 1902 the average had dropped to 3.5% Sn. However, during the first 30 years, this operation from a number of shafts, produced 4470 tonnes of tin metal. After this, only sporadic mining took place on the main and subsidiary lodes until 1953. Meanwhile, both lode and alluvial mining were taking place across the field which covered an area with a 20 km radius, with Herberton being on its ENE rim. This accounted for the balance and bulk of the production from the district.
  The Baal Gammon mine is a historical underground copper mining centre, that has been worked for more than 100 years. In 2005, the smaller holding were consolidated into two larger titles and an open-cut operation initiated in 2011. The mine was initially operated by Kagara Limited in joint venture with the mining title holder, Monto Minerals. Kagara mined high grade Cu-Ag-Sn ore that was trucked to their beneficiation plant at Mount Garnet, which is ~25 km SW of Herberton. Mining was initially at a rate of 250 000 tpa with a 3.7:1 stripping ratio. However, a severe spill of contaminated water in early 2012 led to the mine being closed for remediation. Soon after, Kagara Limited was put into receivership due to other financial difficulties, and its assets sold by the liquidator to a Chinese company, Snow Peak Mining, who recommenced operations at Baal Gammon and Mount Garnet in 2014. In March 2017, Snow Peak Mining, through its Australian subsidiary Consolidated Tin Mines Limited, relinquished their interest in Baal Gammon. The mine was abandoned in May 2019, following cancellation of the mine operator’s mining lease for compliance issues. As of August 2021, it was undergoing remediation by the Queensland Government as part of its Abandoned Mine Lands Program. Isabel is an un-mined and partially tested resource.

Regional Setting

The Herberton Mineral Field is situated centrally within the Mossman Orogen of North Queensland. This orogen is characterised by the deposition and deformation of voluminous marine sedimentary and igneous rocks on the northeastern Australian continental margin during the Silurian and Devonian. It occupies the northern extremity of the Tasmanides and is positioned generally to the north and NE of the Neoproterozoic to Ordovician Thomson Orogen and east of the Etheridge Province of the pre-Neoproterozoic North Australian Craton. It is elongated north-south and bounded by the Pacific Ocean to the east and the younger Laura Basin cover to the north.

The Mossman Orogen is largely occupied by the Hodgkinson Formation of the Hodgkinson Province that is intruded by granites of the Kennedy Igneous Association (Henderson et al., 2013). The Hodgkinson Province sequence is composed of shallow-marine limestone of the Early Silurian Chillagoe Formation, underlain by Ordovician siliciclastic rocks along the Palmerville Fault which marks the western margin of the Province. The Chillagoe Formation is, in turn, overlain by the Silurian to Late Carboniferous Hodgkinson Formation turbiditic siliciclastics with subordinate limestone, chert and mafic volcanic rocks. The turbiditic siliciclastics include pale to dark or greenish grey, fine to medium-grained, medium to thick-bedded, quartz-intermediate arenite, rhythmically interbedded with siltstone and mudstone, as well as minor conglomerate, and conglomeratic arenite. These turbidites are intercalated with mélange deposits (Barron-Palmer Formation; Withnall and Henderson, 2012), which to the west are interpreted to have been deposited as an abyssal fan (Henderson et al., 2013). The maximum depositional age of the group has been variously estimated at ~482, 463, 454 and 370 Ma, based on dating of detrital zircons (Henderson et al., 2013; Kositcin and Bultitude, 2015), although its minimum age is constrained by the Kennedy Igneous Association.

The Kennedy Igneous Association is composed of Carboniferous to Permian granites batholiths, high-level intrusives and volcanic to sub-volcanic rocks. The granites have been grouped in suites and supersuites, based on petrological character (White et al., 2001). Most batholiths are composites of multiple intrusions. Supersuites identified in the Herberton Mineral Field include, from oldest to youngest, the O'Briens Creek, Ootan and Almaden supersuites. Volcanic units in the Herberton area belong to the Featherbed and Koolmoon Volcanics.

The O'Briens Creek Supersuite is strongly fractionated, and includes the Herberton Hill and Jumna granites (Champion, 1991). It typically comprises pink to yellow alkali feldspar granite with associated granophyre, microgranite, topaz-bearing aplite and silexite, reflecting its fractionated nature (Johnston and Black, 1986). Dating has constrained the age of this supersuite to ~335 to 317 Ma in the mid-Carboniferous (Cheng et al., 2018).

The Ootann Supersuite is widespread in the Herberton Mineral Field (Champion, 1991), and is represented by the Late Carboniferous ~310 to 302 Ma Watsonville Granite (Cheng et al., 2018). It is a medium- to coarse-grained granite and commonly contains veins of aplite and patches of pegmatite (Blake, 1972).

The Almaden Supersuite is composed of granodiorite with minor diorite, and includes the Kalunga Granodiorite south of the Isabel deposit. This granodiorite is not mineralised and contains medium-grained quartz, zoned oligoclase-andesine, turbid orthoclase and biotite and has a hypidiomorphic granular texture (Sheraton and Labonne, 1978).

The Mid to Upper Carboniferous Featherbed Volcanics are split into the Old and Young Featherbed Volcanics. The Old Featherbed Volcanics are dated at 325 to 317 Ma (Cheng et al., 2018), and comprise dacitic to rhyolitic ignimbrite and minor andesitic tuff (Cheng et al., 2018; Mackenzie, 1993), whilst the Young Featherbed Volcanic unit is constrained at ~310 to 275 Ma (Cheng et al., 2018), and consists of porphyritic rhyolite, rhyolitic ignimbrite, volcanic breccia, microgranite, and minor dacite (Cheng et al., 2018; Sheraton and Labonne, 1978).

The Permo-Carboniferous Koolmoon Volcanic Group is made up of the Late Carboniferous to Lower Perian Walsh Bluff, Glen Gordon and Lower Permian Slaughter Yard Creek Volcanics (Donchak and Bultitude, 1998). It consists of tuff, tuffaceous sandstone and siltstone, felsic lava flows, and agglomerate (Blake, 1972). Despite being grouped with the volcanics, and including a series of rhyolitic flows, and volcaniclastic rocks, the ~284 Ma Slaughter Yard Creek Volcanics also contain other intrusive rocks that comprise quartz-feldspar porphyry and felsic/rhyolite dykes, (Cheng et al. 2018; Kumar et al., 2022).


Baal Gammon

The Baal Gammon deposit is developed along the contact between the Hodgkinson Formation and a quartz-porphyry dyke, the UNA Porphyry. The Hodgkinson Formation at Baal Gammon is the oldest geological unit in the area. It comprises cross-bedded, fine- to coarse-grained, greenschist facies meta-sandstone that was gently folded, dipping at ~10 to 20°S to SW. It is crosscut by a series of low-angle thrusts and steeply dipping transcurrent faults, and is intruded by the hydrothermally altered, tin-bearing, UNA Porphyry, and by barren quartz veins. The entire sequence is crosscut by quartz-feldspar porphyry dykes, mapped as the Slaughter Yard Creek Volcanics (Donchak and Bultitude, 1998). The meta-sandstone in the open pit at Baal Gammon is strongly jointed and fractured, altered, and silicified, with muscovite growth parallel to joints and fractures, and near the UNA Porphyry contact, contain garnet and andalusite, indicating contact metamorphism.

The UNA Porphyry has a granitic in composition, and occurs as a dyke intruding the Hodgkinson Formation and dipping shallowly to moderately south. It is ~1200 m in length, with an average thickness of 15 m, but has an irregular shape,net, and a suite of steeply dipping, NNW trending faults crosscut both the Hodgkinson Formation and the UNA Porphyry. At the Baal Gammon open pit and surrounding hills, the UNA Porphyry is strongly altered, and has a vuggy texture. Less altered sections comprise quartz phenocrysts in a finer grained mass of feldspar, quartz and minor biotite, with ~50% quartz, 10% alkali feldspar, 5% plagioclase and lesser biotite, chlorite, garnet and sulphides, with a granophyric groundmass. The subhedral, porphyritic quartz crystals include embayments of fine-grained material similar in composition to the surrounding matrix, and commonly have a spongy texture. The embayment textures are interpreted to have formed during decompression and ascent of the porphyritic body, when the quartz crystals were partially dissolved (Chang and Meinert, 2004). Most of the plagioclase and alkali feldspar are altered to sericite, and biotite is partly altered to chlorite.

The entire sequence is crosscut by felsic porphyry dykes of the Slaughter Yard Creek Volcanics. At shallow levels, these dykes are of variable thickness, subvertical and trend NW. Three different dyke phases were identified based on texture, composition, and overprinting relationships. The oldest comprise an eastward trending set of coarse-grained, quartz-feldspar porphyry which varies from a few metres thickness in the western wall of the pit, to almost 10 m in the eastern wall. It has up to 20 mm phenocrysts of plagioclase and quartz, in a fine-grained groundmass of quartz, plagioclase, K feldspar and minor biotite. The second phase forms a medium-grained porphyritic dyke composed of plagioclase, quartz, K feldspar, biotite and chlorite. Textures are consistent with phase postdating the first phase. The second phase is only exposed only on the eastern side in the pit where it trends SE, where biotite and chlorite are secondary alteration products in the groundmass. The youngest phase comprises shallow intrusive rhyolite dykes in the northeastern part of the deposit.

The Hodgkinson Formation meta-sedimentary rocks in the Baal Gammon deposit area are open folded and dip to the SW with a fold axis that plunges gently towards 220°. No tectonic foliation has been recognised, although the metasedimentary rocks are affected by bedding-parallel fractures and shears that dip at 20 to 40°SW. These fractures and shears also affect the other rocks within the deposit area, and are accompanied by a set of conjugate, sub-vertical, NE and NNW trending joints. A series of moderately east dipping and NNW striking reverse faults have displaced the UNA Porphyry.

The hypogene mineralisation at the Baal Gammon deposit has been subdivided into two stages, early,
• stage I tin oxide, characterised by strong silicification of the meta-sandstone to form a silica cap surrounding the UNA Porphyry, whilst at deeper levels, the feldspars of the porphyry were altered to sericite and cassiterite was precipitated as 100 to 600 µm sized, zoned, euhedral crystals within the same porphyry. Stage I was followed by the
• stage II massive sulphide phase accompanied by sulphide veins and breccia infill. The massive sulphides and mineralised brecciated meta-sandstone occur along the contact with the UNA Porphyry, both of which are also crosscut by sulphide veins. Chalcopyrite containing inclusions of sphalerite is the most abundant sulphide at the Baal Gammon deposit, and occurs in association with pyrrhotite to form the massive sulphides. The early cassiterite phase has altered to In-rich stannite in the massive sulphides. Element composition maps indicate that the stannite is rich in Zn, Sn and In.

A supergene cap is evident in the open pit and the surrounding rocks. It has a wedge shape and was developed above the mineralised meta-sandstone. Iron oxides and silica dominate, with infill of malachite and azurite to form a vuggy to honeycomb texture. Fine-grained covellite occurs as infill surrounding azurite. Close to the deposit, the supergene mineralisation is located above an east dipping fault.

Indium is an important by-product at the Baal Gammon deposit, and is closely related to the UNA Porphyry and the massive sulphide mineralisation. The highest grades were found in semi-massive sulphide veins within the porphyry, and along the contact between the porphyry and the Hodgkinson Formation. Resource models indicate an average grade of ~63 ppm In within the deposit. Element-element correlations samples from diamond-drill core at Baal Gammon show a strong positive correlation between In and Cu (r = 0.9) and Ag (r = 0.8) and a moderate correlation with Fe (r = 0.6), Bi (r = 0.5) and Zn (r = 0.4). The Cu-rich parts of the deposit (i.e., >0.1% Cu) have an average grade of ~40 ppm In, increasing to as much as 1140 ppm In in sulphides along the UNA Porphyry and Hodgkinson Formation contact. High-grade >50 ppm Ag mineralisation contains an average of ~110 ppm In, with the highest In grades being observed within the porphyry or at the contact of the meta-sediments with the porphyry (Kumar et al., 2022).


Isabel

The Pb-Zn-Ag-Sn-In mineralisation of the Isabel deposit is hosted by brecciated quartzite of the Hodgkinson Formation, which is intruded by dolerite, quartz-feldspar porphyry and feldspar porphyry dykes. The host quartzite unit is part of a metasedimentary sequence dominated by poorly sorted, coarse- to fine-grained quartz-feldspar arkosic sandstone, containing chert and rhythmic intercalations of meta-siltstones, and is variably iron-stained at the surface. The quartz grains within the sandstone are recrystallised and have polygonal textures and undulose extinction. Beneath the surface iron-staining, the meta-sandstone is dark green and chlorite-sericite altered. The meta-sandstone host to the deposit is brecciated, with both fault and hydrothermal breccia. The fault breccia is not mineralised and comprises 'jigsaw-fit' angular meta-sedimentary clasts set in a fine-grained quartz, feldspar, chlorite and muscovite matrix. In contrast, the hydrothermal breccia, which also has 'jigsaw-fit' angular clasts, but has a matrix of significant fine-grained sulphide mineralisation. This latter breccia has a gossan cap composed of iron oxide and clay. The Hodgkinson Formation is contact with the Herberton Hill Granite to the south.

The igneous rocks in and around the Isabel deposit include the Herberton Hill Granite, Slaughter Yard Creek Volcanics, and porphyry dykes. The contact between the Hodgkinson Formation and the Herberton Hill Granite has a NE trend. The most exposed Herberton Hill Granite phase is a coarse-grained, pink, leucocratic monzogranite with traces of primary biotite and mica that is exposed at the southeastern section of the Isabel deposit. It is moderately weathered in outcrop, with plagioclase and K feldspar altered to clay, and iron oxides formed at quartz grain boundaries.

The porphyry dykes comprise feldspar porphyry, quartz-feldspar porphyry and dolerite. Only the quartz-feldspar porphyry and dolerite outcrop. The quartz-feldspar porphyry is composed of plagioclase altered to sericite and embayed quartz. Altered feldspar crystals are surrounded by muscovite, and locally contains carbonate filled vugs. The matrix includes fine-grained quartz, plagioclase and chlorite, with opaque minerals replacing feldspar and the groundmass, which has a granophyric texture and comprises quartz, altered feldspar and chlorite. The dolerite dyke is fine-grained and chlorite-sericite altered. It contains veins and late infill of vugs by fine-grained quartz, plagioclase and carbonates. Pyroxene and plagioclase have been altered to chlorite.

The Slaughter Yard Creek Volcanics occur as shallow level porphyry dykes and equivalent extrusive rock units. The latter include breccia and welded tuff, intercalated with thinly bedded siltstone and sandstone. The breccia is made up of angular, up to 10 cm across, sedimentary fragments composed of recrystallised quartz and muscovite, set in a matrix of silica, sericite, albite and quartz. The welded tuff is light brown to grey-green and has a eutaxitic texture with vugs. The feldspar grains in the welded tuff are angular and have been replaced by chlorite, whilst the quartz grains are rounded with preserved embayments. The siltstone and sandstone are creamy white, and contain abundant angular quartz fragments. Field evidence is said to suggests that the mineralisation was positioned close to the contact between the metasediments and the quartz-feldspar porphyry dyke (Kumar et al., 2022).

In the Isabel deposit area, the Hodgkinson Formation dips at 75°E, and is cut by four sets of lineaments, interpreted to represent faults, striking at 327°, 45°, 275° and 300° as four respectively younging generations. Quartz-feldspar porphyry and dolerite dykes parallel the first generation lineaments, whilst the contact between the Herberton Hill monzogranite and Hodgkinson Formation is interpreted to be a fault and parallels the second generation lineaments. The latter orientation correlates with that of the tin mineralisation at the Isabel deposit. The intersection between the first and fourth lineament generations is characterized by intense brecciation, and the deposition of lead–zinc sulphides mineralisation (Robinson, 1983)

The mineralisation at Isabel comprises both polymetallic veins and breccia hosted by the Hodgkinson Formation. Sphalerite, which contains inclusions of chalcopyrite, is the dominant sulphide mineral at Isabel. The polymetallic veins occur as two sets, as follows:
 • Type I - comprising disseminated cassiterite and sphalerite with chalcopyrite inclusions, crosscut by chalcopyrite-pyrrhotite veins. The cassiterite grains are fractured and show early stages of alteration. This early cassiterite is partially replaced by chalcopyrite, giving the veins a slightly porous texture. Complete cassiterite alteration has not been observed, with only dissolution and replacement textures evident.
 • Type II - consisting of sphalerite, galena and stannite. The galena occurs as idiomorphic crystals with triangular pits evident under reflected light. The sphalerite and quartz veins crosscut the galena, and the sphalerite contains stannite inclusions. Stannite occurs along the boundary of sphalerite and galena, but mostly in sphalerite.

Resource models for the Isabel deposit indicate an average indium grade of ~370 ppm (Red River Resources Limited., ASX announcements, 2020). The Sn- and Cu-rich parts of the deposit (i.e., >1% Cu, and >0.2% Sn) have average indium concentrations of ~1140 ppm, with a maximum recorded concentration of up to 2030 ppm. The indium concentration in the Zn ore zones locally reaches 3170 ppm. Element-element correlations, based on geochemical assay results in diamond-drill core indicate that indium has a strong positive correlation with Cu (r = 0.7), Sn (r = 0.6) and Zn (r = 0.6), and a weak positive correlation with Ag (r = 0.4).


Mineral Resources

JORC compliant Mineral Resources at Baal Gammon, as at January 2012 were (Monto Minerals ASX Release):
Global Resource at a 0.2% Cu cut-off
  Indicated Mineral Resource - 2.769 385 Mt @ 1.0% Cu, 40 g/t Ag, 0.2% Sn, 38 g/t In;
  Inferred Mineral Resource - 30.636 Kt @ 0.6% Cu, 18 g/t Ag, 0.1% Sn, 63 g/t In;
  TOTAL Mineral Resource - 2.80 Mt @ 1.0% Cu, 40 g/t Ag, 0.2% Sn, 39 g/t In;
including a high grade resources zone that was mined
  Indicated Mineral Resource - 825.629 Kt @ 2.5% Cu, 96 g/t Ag, 0.4% Sn, 96 g/t In;
  Inferred Mineral Resource - 3.622 Kt @ 2.7% Cu, 94 g/t Ag, 0.4% Sn, 146 g/t In;
  TOTAL Mineral Resource - 829.251 Kt @ 2.5% Cu, 96 g/t Ag, 0.4% Sn, 96 g/t In.

NOTE: The information in this record is drawn from Kumar et al. , 2022; 2023), supplemented by the Geoscience Australia Stratigraphic database and other sources.

The most recent source geological information used to prepare this decription was dated: 2023.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


Baal Gammon

  References & Additional Information
   Selected References:
Allchurch, J.,  2012 - Herberton Tin Project Baal Gammon Copper Project: in    Monto Minerals Presentation, January 2012,    20p.
Kumar, A., Sanislav, I.,Martin, L., Aleshin, M. and Dirks, P.,  2024 - Genesis of copper mineralization in the polymetallic tin deposits from the Herberton Mineral Field, Queensland, Australia: in    Mineralium Deposita   v.59, pp. 291-311.
Kumar, A.A., Sanislav, I.V. and. Dirks, P.H.G.M.,  2022 - The geological setting of the indium-rich Baal Gammon and Isabel Sn-Cu-Zn deposits in the Herberton Mineral Field, Queensland, Australia: in    Ore Geology Reviews   v.149, 19p. doi.org/10.1016/j.oregeorev.2022.105095.
Kumar, A.A., Sanislav, I.V., Cathey, H.E. and. Dirks, P.H.G.M.,  2023 - Geochemistry of indium in magmatic‑hydrothermal tin and sulfide deposits of the Herberton Mineral Field, Australia: in    Mineralium Deposita   v.58, pp. 1297-1316. doi.org/10.1007/s00126-023-01179-7.


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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